Aspects and embodiments of the invention are most generally directed to optical systems/apparatus and methods for designing and/or making said optical systems/apparatus. More particularly, aspects and embodiments of the invention are directed to a see-through optical display apparatus and method for designing and/or making said see-through optical display apparatus.
Wearable displays, such as head-worn displays (HWDs), represent the newest entry into the ever-evolving augmented reality market. Packaging constraints for HWDs align with the constraints of other devices that are worn on one's head. This necessitates such devices to be lightweight and compact, meaning using a minimum number of optical elements and employing unique packaging geometries. The problem remains that when the number of optical elements is reduced and non-rotationally symmetric geometries are used, the resulting optical aberrations are too great to correct with rotationally symmetric optical surfaces. Because the design problem of HWDs is so highly constrained (element count, geometry), the surface shapes play an extremely important role.
When starting an optical design, there are three critical parameters that need to be well-defined: the operational waveband, the aperture stop size, and the field of view. The waveband is important because it dictates the materials one can use, and, for a visual system that requires an external aperture stop, lateral chromatic aberrations are often the limiting aberrations of the system. The remaining two parameters often fight against one another according to the Lagrange invariant, where a given value for the Lagrange invariant reflects the overall complexity of the design. A large aperture stop requires a smaller FOV, and vice-versa.
A disadvantage of rotationally symmetric reflective systems is that they are obscured, which decreases the total intensity of light and introduces diffraction effects at the image plane. Designers can use a variety of strategies to make reflective systems unobscured: 1) the aperture stop can be offset from the mechanical axis, 2) the FOV can be biased, meaning a portion of the off-axis fields are considered the active fields for the system, 3) a combination of 1) and 2), or 4) the surfaces themselves can be tilted. For systems with rotationally symmetric surfaces, the latter most method is typically avoided because tilting powered surfaces results in optical aberrations such as field-constant astigmatism and coma that may not be balanced using rotationally symmetric surfaces.
Another packaging constraint for HWDs is the requirement that they fit around the facial structures near the eye. The distance from the entrance pupil of the optical design, which will be coincident with the entrance pupil of the eye, to the closest design feature (i.e., optical element, detector, microdisplay, etc.) must be great enough to clear the brows, nose, and/or cheek bones.
The inventors have recognized the benefits and advantages to be realized by a see-through optical display apparatus that addresses the aforementioned disadvantages and shortcomings, the especial benefits and advantages of such a see-through optical display apparatus in the form of a head worn display, a detailed and efficient method for designing and making such see-through optical display apparatus and HWDs, and techniques for analyzing the performance of such see-through optical display apparatus and HWDs. These benefits and advantages are realized by the embodied invention as described herein below with reference to the figures and in the appended claims.